1. Technical Field
This disclosure relates to a backlight device.
2. Description of the Related Art
In recent years, LEDs (light-emitting diodes) have been introduced as backlight sources for liquid crystal display devices to save energy. For example, there is known a backlight device that includes a plurality of LEDs arranged on a substrate having a planar shape. FIG. 11 illustrates a plan view and a cross-sectional view along D-D′ line of a backlight device 900. The backlight device 900 includes a substrate 901 having a planar shape and a plurality of LEDs 902 arranged on the substrate 901. The LEDs 902 are arranged at a uniform density on the substrate 901. The backlight device 900 is placed parallel and close to a liquid crystal panel 950 indicated by a dashed line in such a manner as to face the back surface of the liquid crystal panel 950, whereby a liquid crystal display device 960 is formed.
The characteristics of LEDs, such as, for example, brightness, chromaticity, and deterioration rate, vary depending on the temperature of the LEDs and the current supplied to the LEDs. Accordingly, in order to extend the lifetime of LEDs while achieving desired brightness or chromaticity, it may be necessary to optimally control, for example, current supplied to the LEDs in accordance with the temperature thereof. When current is supplied to an LED, the LED generates heat. Although the degree of heat generation is lower than that in the case of an incandescent bulb or the like, because of such heat generation, the temperature of an area in which LEDs are densely arranged is more likely to increase than the temperature of an area in which LEDs are sparsely arranged. Therefore, the quality and lifetime of the LEDs in the densely arranged area are more likely to decrease than the LEDs in the sparsely arranged area. To this end, it is important, in terms of image quality, to prevent increase in the temperature of an area in which LEDs are densely arranged. Although the temperature of an area in which LEDs are sparsely arranged is less likely to increase, it is important to note that the brightness in the sparsely arranged LED area is inherently low. To this end, it is important, in terms of image quality, to prevent further decrease in the brightness in an area in which LEDs are sparsely arranged. Therefore, there is a need for a backlight device that can control current applied to LEDs based on the characteristics of the areas in which LEDs are arranged.